Exhaust gas driven turbochargers include a rotating shaft carrying a turbine wheel and a compressor wheel, which is rotatably supported within a center housing by one or more lubricated bearings (e.g., oil lubricated). During operation, exhaust gas from an internal combustion engine drives a turbocharger's turbine wheel, which, in turn, drives the compressor wheel to boost charge air to the internal combustion engine. Through proper bearing lubrication, a turbocharger's rotating assembly can readily withstand rotational speeds in excess of 100,000 rpm.
As operational conditions change, a turbocharger can experience significant forces. For example, a sudden increase in exhaust flow can generate so-called “thrust forces”. To help transfer and diminish the detrimental impact of thrust forces, clearances between various components allow for formation of protective lubricant layers. For example, bearings, which are inherently affected by thrust forces, typically include end features referred to as “thrust pads” that cooperate with lubricant to transfer axial thrust forces.
A conventional bearing typically includes asymmetric thrust pads where the asymmetry arises from differences between turbine end features and the compressor end features. Such asymmetry introduces variation (e.g., in fabrication techniques) and can require special markings to ensure proper assembly of center housing components.
Another bearing thrust pad issue pertains to lubricant leakage and, more generally, lubricant flow patterns. For example, a conventional thrust pad can allow lubricant to leak from a shaft journal to a center housing drainage well in a manner that by-passes a thrust pad surface. In this example, the lubricant does not contribute to the bearing's thrust load capacity. To ensure adequate load capacity, such a system may require increased lubricant flow, which, in turn, increases power loss (e.g., parasitic power loss, etc.).
Various exemplary technologies described herein pertain to bearing thrust pads, which can address thrust pad issues by promoting beneficial lubricant flow patterns.